Quantum Correlations In A Cavity–magnon System With Feedback Control

In recent years,ferrimagnetic systems have become a new quantum technology platform for studying the interaction between light and matter,owing to their high spin density and low damping rate.In hybrid systems containing magnons,magnons induced by the collective excitation of a large number of spins can couple with different modes.The property has attracted extensive attention of many researchers and resulted in a research direction dubbed cavity magnonics.Many interesting phenomena have been discussed in cavity magnonics,such as magnetically induced transparency,magnon blocking,slow light effect,etc.Here,we are concerned about the quantum effects between two massive ferromagnetic spheres separated into two microwave cavities in a cavity-magnon system.Previous studies have shown two possible schemes to generate the correlation between two magnons.The first scheme is to introduce necessary nonlinearities into the system,such as magnetostrictive interaction,Kerr effect,etc.,and the other is to inject external quantum resources into the system,such as squeezed vacuum fields,etc.Here,we propose a new scheme that uses feedback control to generate quantum correlations between two magnons without considering any nonlinear interactions.The specific design idea is that: adding feedback loops between two separate microwave cavities,allowing the output of one cavity field to regulate the input of the other cavity field,which in turn changes the input noise characteristics of the cavity field.Moreover,it is possible to control the number of feedback loops by adjusting the feedback gain in the loop.The quantum correlation between two magnons in both symmetric and asymmetric cases of the system structure is discussed with numerical analysis.We found that the entanglement between the two magnons is stronger and more robust to temperature under double feedback loops,and the quantum steering between the two magnons has one-way nature in the single feedback loop.The paper consists of four chapters as follows:In Chapter 1,we introduce the basic theoretical knowledge,including feedback control,the input-output relation of cavity field,the Routh-Hurwitz criterion and the covariance matrix of the Gaussian state.In Chapter 2,we review the generation of fundamental interactions in cavity-magnon systems.In Chapter 3,we present the specific work of our study,which discusses the quantum correlation between the two magnons in a cavity-mangnon system with added feedback control.And we make a summary in the last chapter.